The present invention relates to a sorter that is attached to an image forming apparatus such as a copying machine, a printing machine or a laser beam printer and receives in each bin multiple copy sheets ejected from the image forming apparatus after sorting and grouping them, and more particularly, to a sorter with stationary bins wherein a plurality of sorters can be linked.
A type of a sorter sorting and grouping automatically a plurality of sheets (copy sheets) ejected from an image forming apparatus such as a copying machine includes a type of stationary bins, a type of all movable bins and type of each opening and moving bin.
In the case of a type of stationary bins, when making multiple sets of recorded sheets from multiple originals in an image forming apparatus, sheets ejected from the image forming apparatus are taken successively in a sheet-receiving portion of the sorter, then moved to the transport portion, and taken into each bin to be bound in a proper sequence by the action of a branch guide (a ranch gate) provided at a sheet-inlet of each bin on an allocating unit composed of multiple bins, on a half way of transport, thus recorded sheets of multiple sets corresponding to the maximum number of bins are arranged methodically.
The sorters of a type of stationary bins are widely used for high speed copying machines of a console type because of advantages that the number of sheets to be taken in bins is relatively large, responding speed is high and a plurality of sorters can be linked. For example, each of 20 bins for sorting or grouping can take in about 50 sheets for stacking.
On the other hand, a sheet finisher provided with a stapler unit that staplers sheets ejected from a copying machine or the like includes;
(1) a sheet finisher that is used in combination with a device such as an automatic original-transport unit of a circulating type (RDH) and staples each group of sheets,
(2) a device wherein a stapler unit is provided on a relatively simple sorter of a type of movable bins {Japanese Patent Publication Open to Public Inspection No. 43457/1989 (hereinafter referred to as Japanese Patent O.P.I. Publication)}, which is a sorter in which a stapler unit stapling sheets in each bin is arranged to be movable back and forth against the bin,
(3) a sheet finisher wherein a stationary stapler unit is provided on each bin and each bin is moved to the stapling position for stapling a bundle of sheets, and
(4) a sheet finisher of a sorter disclosed in Japanese Patent O.P.I. Publication No. 244869/1987 wherein a bin holding thereon sheets is moved for stapling to the position capable of stapling, and stapling for other bins requires bin movement and vertical movement of a stapler unit.
A sheet ejected from the image forming apparatus mentioned above and received by the above-mentioned sorter of a type of stationary bins is transported at high speed through the horizontal path and the vertical path both in the sorter into each bin mentioned above or onto a non-sort tray.
A plurality of bins in the sorter mentioned above are generally composed of the maximum of 20 bins. When sorting sheaves of sheets in quantity of 20 or more in bins, therefore, a plurality of sorters need to be linked together so that sheets ejected from an image forming apparatus may be sorted and received successively in each bin of the sorters.
In conventional sorters of a multiple linkage type, they have been used so that the bins of the first sorter may follow the bins of the second sorter. Namely, when sorting 21 sets of recorded sheets on sorters each consisting of 20 bins, 21st set of recorded sheets is received by the uppermost bin of the second sorter only after one through 20 sets of recorded sheets have been received by 20 bins of the first sorter in succession downward from the top bin.
In the case of a sorter provided with a stapler unit, stapling for recorded sheets in each bin is conducted downward only after all recorded sheets in predetermined quantity in each bin have been received by the bin. Therefore, it takes a long time to finish stapling, resulting in a long down time and poor productivity for the total operation.
Now, it is assumed that t.sub.1 represents a copying interval, t.sub.2 represents a stapling interval, and stapling for the first bin is started after a copy sheet has been ejected into the first bin. Incidentally, the relation of t.sub.2 &gt;t.sub.1 is generally normal.
In the second sorter, stapling for the 21st set of recorded sheets is started after copy sheets have been ejected into the 21st bin, similarly to the above.
Under the assumption that L.sub.1 represents a distance from an image forming apparatus to the first bin, L.sub.2 represents a distance from the image forming apparatus to the 21st bin, V represents a sheet transport speed and N.sub.1 represents the number of sets of copy sheets which is 20 or less, time T required to cover the finish of copy operation in an image forming apparatus through the finish of stapling is as follows. EQU T.sub.1 =L.sub.1 /V+t.sub.2 .times.N.sub.1 -t.sub.1 .times.(N.sub.1 -1)(1)
When N.sub.2 represents the number of sets of copy sheets which ranges from 20 sets to 40 sets, the time required for the first sorter is as follows. EQU T.sub.2 =L.sub.1 /V+t.sub.2 .times.30-t.sub.1 (N.sub.2 -1) (2)
The time required for the second sorter is as follows. EQU T.sub.3 =L.sub.2 /V+t.sub.2 (N.sub.2 -20)-t.sub.1 (N.sub.2 -20)-t.sub.1 .times.(N.sub.2 -21) (3)
In this case, time required T is represented by T.sub.2 or T.sub.3 whichever is greater.
It has been desired to shorten the aforementioned required time T for reducing the down time which makes it impossible to take out all sets of copy sheets for use because of unfinished stapling even after the finish of copying.